From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2B20DC43467 for ; Fri, 9 Oct 2020 15:31:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D931F22261 for ; Fri, 9 Oct 2020 15:31:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ccIpZJ+v" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389309AbgJIPaw (ORCPT ); Fri, 9 Oct 2020 11:30:52 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:20434 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389295AbgJIPav (ORCPT ); Fri, 9 Oct 2020 11:30:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1602257449; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=HhcoI+2TUmCVBTasDOAADDA46P10/1EEE1A+Q+QUMXg=; b=ccIpZJ+v87vEK+AltHe4+Rc2VSIxJ6OznRNplx2UR1QhLZvwrrGcTnZX5dgBCspiscU47u LIk5/jmhFssV628Jj/QL8sjpFOlj0uLyLjXWvXx/+IThbdGyrJZuRKPF64d/VCsPipp74L rUussT6PADHJfCxDXDQACNiBWBuHrWs= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-88-VMDdQT3wMG67TRXr_ZVgIw-1; Fri, 09 Oct 2020 11:30:47 -0400 X-MC-Unique: VMDdQT3wMG67TRXr_ZVgIw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B90BA83DBC5; Fri, 9 Oct 2020 15:30:40 +0000 (UTC) Received: from ovpn-66-175.rdu2.redhat.com (unknown [10.10.67.175]) by smtp.corp.redhat.com (Postfix) with ESMTP id 03BE710021AA; Fri, 9 Oct 2020 15:30:38 +0000 (UTC) Message-ID: <07fffca72fdd585a96ab8c45761c1ea223dc24f2.camel@redhat.com> Subject: Re: [tip: locking/core] lockdep: Fix lockdep recursion From: Qian Cai To: paulmck@kernel.org Cc: "Peter Zijlstra (Intel)" , Steven Rostedt , Ingo Molnar , x86 , linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org, Linux Next Mailing List , Stephen Rothwell , Boqun Feng Date: Fri, 09 Oct 2020 11:30:38 -0400 In-Reply-To: <20201009135837.GD29330@paulmck-ThinkPad-P72> References: <160223032121.7002.1269740091547117869.tip-bot2@tip-bot2> <20201009135837.GD29330@paulmck-ThinkPad-P72> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-next@vger.kernel.org On Fri, 2020-10-09 at 06:58 -0700, Paul E. McKenney wrote: > On Fri, Oct 09, 2020 at 09:41:24AM -0400, Qian Cai wrote: > > On Fri, 2020-10-09 at 07:58 +0000, tip-bot2 for Peter Zijlstra wrote: > > > The following commit has been merged into the locking/core branch of tip: > > > > > > Commit-ID: 4d004099a668c41522242aa146a38cc4eb59cb1e > > > Gitweb: > > > https://git.kernel.org/tip/4d004099a668c41522242aa146a38cc4eb59cb1e > > > Author: Peter Zijlstra > > > AuthorDate: Fri, 02 Oct 2020 11:04:21 +02:00 > > > Committer: Ingo Molnar > > > CommitterDate: Fri, 09 Oct 2020 08:53:30 +02:00 > > > > > > lockdep: Fix lockdep recursion > > > > > > Steve reported that lockdep_assert*irq*(), when nested inside lockdep > > > itself, will trigger a false-positive. > > > > > > One example is the stack-trace code, as called from inside lockdep, > > > triggering tracing, which in turn calls RCU, which then uses > > > lockdep_assert_irqs_disabled(). > > > > > > Fixes: a21ee6055c30 ("lockdep: Change hardirq{s_enabled,_context} to per- > > > cpu > > > variables") > > > Reported-by: Steven Rostedt > > > Signed-off-by: Peter Zijlstra (Intel) > > > Signed-off-by: Ingo Molnar > > > > Reverting this linux-next commit fixed booting RCU-list warnings everywhere. > > Is it possible that the RCU-list warnings were being wrongly suppressed > without a21ee6055c30? As in are you certain that these RCU-list warnings > are in fact false positives? I guess you mean this commit a046a86082cc ("lockdep: Fix lockdep recursion") instead of a21ee6055c30. It is unclear to me how that commit a046a86082cc would suddenly start to generate those warnings, although I can see it starts to use percpu variables even though the CPU is not yet set online. DECLARE_PER_CPU(unsigned int, lockdep_recursion); Anyway, the problem is that when we in the early boot: start_secondary() smp_init_secondary() init_cpu_timer() clockevents_register_device() We are taking a lock there but the CPU is not yet online, and the __lock_acquire() would call things like hlist_for_each_entry_rcu() from lookup_chain_cache() or register_lock_class(). Thus, triggering the RCU-list from an offline CPU warnings. I am not entirely sure how to fix those though.